Starlight and the Shifted Six
It's a nice summer day in ponyville and ponies were out and about. Some minding their own business while others are talking with each other.
It is here that we find Starlight Glimmer heading over to Twilight's castle in an excited rush. Why? Because she discovered a new spell that swaps personalities, she discovered this spell by accident after swapping Rarity and Rainbow Dash while trying an unrelated spell at the same castle.
Starlight would make her way into the castle and head over to the library. She then barges into the library room, only to find that all of Twilight's friends were there as well as Twilight herself.
"Hiya Starlight!" Pinkie says cheerfully.
Starlight would wave at them then say "oh um hi, can I speak to Twilight?".
"Sure ya can sugarcube, come on in." Applejack said.
Starlight would nod then walk into the room.
"So what do you need me for Starlight?" Twilight asks her.
" Oh um I discovered a new spell that swaps personalities and I'd like to test it... If that's ok with you girls." Starlight said.
Starlight wasn't expecting the immediate "sure" from Twilight and co. So she gets ready to use her spell.
"Okay I'm here goes." Starlight says as she gets the spell ready.
She would then cast her spell which unknown to her backfires and teleports her out the room, the others watching in confusion and horror.
When Starlight eventually woke up she found herself in a library that was built within a tree.
Her only reaction to this was just one word, "Whoops..."
Starlight would then panick for a little while knowing full well she messed up the spell, Once she calmed down, she looked around in the library for it's owner but nobody was around aside from a pony that looked almost like pinkie pie but her mane was flat and she was a darker pink.
Starlight had noticed that the other Pinkie's cutie mark was an open book instead of the three balloons that the pinkie she knows has.
Starlight had decided to go speak with her, curious to see how'd she react.
"Um hi pinkie, have you seen twilight anywhere?" Starlight asked the pinkie pie look alike.
"My name is actually Pinkamena Dianne Pie but please call me either Dianne or Pinkamena." The look alike responds.
"Oh sorry you look a lot like one of my friends." Starlight said.
Pinkamena sighs then adjusts her reading glasses, she then says "I see, I'm going to guess you're from another universe aren't you?"
"Well I think so, I was trying out a new spell that was supposed to swap personalities but I have no idea how I got here.." Starlight says as she paces back and forth.
"Calm yourself miss, perhaps one of my friends can assist you. In fact you should walk around town and at least get your bearings." Pinkamena said.
"Oh that's a great idea! Thanks Pinkie er I mean Pinkamena. Oh and my name is Starlight Glimmer." Starlight says before she leaves the tree library.
After leaving the library Starlight notices that Ponyville seemed almost the same the difference being that every pony she saw acted in a different way, she decides to make her way to Sugarcube Corner to see if it has changed at all.
On her way she'd try her best to look around just in case the town's layout was different. She unfortunately was a little too busy sightseeing to realize that she had bumped into somepony.
"Hey watch it!" The yellow pegasus she bumped into says clearly upset.
"Flutterbold please calm down..." The cyan mare next to her says in a near whisper.
Starlight had to do a triple take to make sure she wasn't seeing things but right in front of her was both Fluttershy and Rainbow Dash, only with their personalities swapped or is the case as Starlight notices that Flutterbold had a Wonderbolts uniform on but with the hood down, Rainbow on the other hoof seemed like if she had been shy all her life.
"Oh um Sorry about that Flutterbold." Starlight says in a careful manner hoping she didn't get Fluttersky's name wrong.
"It's fine, just be more careful ok?" Flutterbold says as her friend simply nods.
"I'll make sure to be, oh um who's your friend by the way." Starlight says as she figured she'd play along so she'd not seem too off putting.
"oh i'm Prism Shine, it's nice to meet you." Prism Shine said.
"Heh same here, Name's Fluttersky but you already knew that. What's yours?" Flutterbold says as she fixes her goggles that were hanging on her neck.
"I'm Starlight Glimmer, it's nice to meet you too, can you tell me where Sugarcube Corner is?" Starlight said.
The two mares looked at Starlight as if she grew a second head somehow. Flutterbold then says, " Dunno what that place is but if you're looking for some kinda bakery try finding Glitter's Sweet Treats, oh and if you see the owner tell her I said hi."
Starlight was surprised by this news but then it made sense, if pinkie is the librarian that means twilight is the party planner. She immediately thanks Fluttersky and Prism Shine and heads off to the "Glitter's Sweet Treats" bakery.
When she made it there she once again did a triple take, inside was what appeared to be Twilight Sparkle bouncing in place as she cheerfully hummed a little tune to herself. Starlight even noticed that her mane was curly in the front but she also had a ponytail and her cutie mark is a balloon with a star within it.
Starlight would then walk up to the counter to get the twilight look alike's attention.
She definitely wasn't expecting said look alike to immediately teleport right next to her and say "Hiya, I'm Glitter Brightstar nice to meet you!" in a peppy tone.
"Um hi?" Starlight says as Glitter inspects her.
"Are you a new pony!? I like when a new pony I've never seen before arrives!" Glitter Brightstar says as she stops inspecting Starlight.
"Well um technically I would be new to you but I'm also not." Starlight said.
Before Glitter Brightstar could ask Starlight any further questions a small purple dragon runs up to Glitter and says "Hey Glitter are you going to take her order soon she's holding up the line."
"Oh right sorry Violet!" Glitter Brightstar says before heading back to the counter.
"So what kinda sweets are you looking for ma'am?" Glitter asks Starlight.
"Oh um I'd like a cupcake please, oh and Flutterbold says hi." Starlight said.
Glitter Brightstar happily gives Starlight a cupcake then says " Yay, Flutterbold is one of my friends and one of my favorite customers, then again all customers who come to my Bakery are my favorites."
"Um how much do I have to pay for the cupcake?" Starlight asks as politely as she could.
Glitter Brightstar giggles then says "well they cost two bits per if you wanted just one. "
"Oh ok" Starlight pulls out two bits then gives it to Glitter.
"Thank you! Come again soon!" Glitter Brightstar says as she bounces in place.
"You're welcome Glitter oh and my name is Starlight Glimmer. It was nice to meet you, goodbye." Starlight says before she leaves, Glitter would wave goodbye as Starlight left the Bakery.
After leaving the Bakery, Starlight wondered how'd she'd get herself back to her universe as she had now realized that she wasn't in the Ponyville she knew. Lost in thought she didn't notice the apple shaped boutique she was about to bump into.
"Ow, I really should watch where I'm going" Starlight says once she bumped into the boutique.
The owner an orange mare with a golden mane done up in a fancy style would walk out the boutique to do her usual shopping before she notices Starlight next to the boutique.
"Oh my goodness dear, are you alright?" The owner says in an accent that reminded Starlight Glimmer of Rarity's own.
"Y-yeah I'm fine I just need to look where I'm going is all." Starlight Glimmer said.
"Oh that's ok dear. My name is Applegem owner of the Jeweled Apple Boutique and it's very nice to meet you." Applegem says cheerfully.
Starlight was dumb founded this was what Applejack became due to her spell!? She stutters before finally introducing herself as she did with the others.
"Oh that's a wonderful name you have there." Applegem said.
"Oh um thanks, I really should be going now." Starlight says as she gets prepared to leave.
Applegem appears to understand then let's Starlight go on her way.
Starlight wanders the Ponyville she found herself in after her spells failure, she wondered if the alternate universe she was in was the result or did she accidentally cast a different spell entirely whatever the case she doesn't know. As she walked many ponies would now start talking about her or even look her way, the attention was getting her nervous that something might have happened but she continued on.
She eventually finds her way back to the Library she found herself in originally this time a bright white mare with a messy purple mane that was wearing a cowboy hat and bandana was talking with Pinkamena. Starlight didn't want to interrupt them but the mare that was talking to Pinkamena notices her.
"Well howdy there, don't be shy stranger." She says in an adopted country accent.
"Oh um sorry, I didn't want to interrupt your conversation." Starlight Glimmer said.
"Nah it's fine darlin', Name's Quartz Bell by the way." Quartz said.
"Oh I'm Starlight Glimmer, nice to meet you." Starlight Glimmer said.
"Sorry to interrupt you two but I'd like to continue my conversation with my friend if you do not mind." Pinkamena says in a monotone which to Quartz ment that she was annoyed.
"Heh whoops sorry pinks" Quartz says before resuming her conversation with Pinkamena who seemed almost pleased with herself.
Starlight simply shrugs then leaves only to almost bump into Glitter Brightstar who wasn't bouncing in place this time and had a more serious look on her face.
"Starlight Glimmer, I'm very happy you got to meet my friends and all but I think it's time for you to go home now..." Glitter says as her horn suddenly glows, Both Pinkamena and Quartz notice this and back away knowing exactly what Glitter is about to do.
"I can't say goodbye?" Starlight said.
"Sorry but your friends miss you, goodbye." Glitter says before casting her Universe Swap Spell on Starlight who actually attempted to block it at first but wasn't quick enough, she was suddenly teleported away.
When Starlight opened her eyes she was right on top of the middle of the huge table that Twilight and friends were gathered around, it was almost like she never left.
"Starlight! What happened are you ok!?" Twilight asks her.
Starlight looks at her then says "You wouldn't believe me if told you."
Author's Note
Glitter Brightstar: Enjoy the story! 
Really... -_-